Revenues at the Taiwanese handset maker HTC has fallen year on year for the 13th month in a row, continuing a downward trend in its growth that began as far back as March 2011 but has accelerated in the past year.

Figures posted on the company's investor site show that for November, revenues were NT$21,230m ($729m, or £457m). That is down 31% on the figure a year ago – though it is an improvement month on month.

The company does not offer monthly profit figures, but its profitability has been slipping along with its revenues. In the third quarter, to the end of September, it made an operating income of just NT$4.9m ($168,000), down by 80% from the year before, as revenues fell by 50%. With revenues for the fourth quarter likely to fall too, HTC may veer on the edge of profitablity – though the company has not so far issued a profit warning.

HTC is struggling to make headway in the phone market after briefly being the biggest smartphone seller in the US in 2010. In the Android market, it has come up against increasingly fierce competition at all price points from South Korea's Samsung. Meanwhile its newest range of HTC 8S Windows Phone handsets – a lower-end challenger – will not go on sale in the US because of "testing delays", it said last week. Instead it will only be selling its top-end HTC 8X Windows Phone device in the US.

The HTC-Apple deal relates to utility patents, and Samsung is arguing that the iPhone maker's willingness to license some patents to HTC means that it should not be granted an injunction against Samsung devices claimed to infringe the same patents.

Meanwhile, data from ComScore shows that HTC has rapidly been losing share in the US market, the world's richest – though not biggest by volume – for smartphones. Its figures for phone ownership in the US in October show that fewer people are using HTC phones: from a peak of just under 15m in use in January 2012, the number now has fallen to just over 14m.

By contrast the number of Samsung phones – both smartphones and featurephones – in use in the US has risen during that period from 59.4m to 61.5m, while iPhone use has risen from just under 30m to 41.6m, according to ComScore's data. Together the two companies are now the most-used phone brands in the US, ComScore says.